1. Technical Field
The present invention relates to devices which can receive user input through a display screen and, more specifically, to a method and a system for controlling the rate of sampling of such user input so as to reduce power consumption and improve processing efficiency in such devices.
2. Related Prior Art
Portable computers are used today in a variety of applications and environments. Many users prefer the convenience of a "laptop" or "hand-held" portable computer to a "desktop" computer or workstation. Some portable computers are general purpose computers which are designed to support the traditional home or office environment, while others may be specifically designed for a particular application, such as tracking production volumes in a factory or inventory levels in a warehouse. As with computers in general, the capabilities (i.e., built-in memory and processing power and speed) of portable computers continue to increase with the passage of time and, as a result, it is likely that the use of portable computers will become even more widespread in the foreseeable future.
Many types or brands of commercially available portable computers allow the user to enter data by interacting with the display screen in a manner generally referred to as "touch screen input." Examples of portable computers that use touch screen input include the so-called "personal digital assistant" (PDA) devices such as the Apple Newton, Motorola Envoy and U.S. Robotics Pilot products. The form and content of touch screen input may vary depending on the choice of software or hardware. For example, in some applications the user may be prompted to select a particular action or menu command by pressing or placing his finger against a corresponding "radio button" that appears on the screen. In other applications, the user may be able to use an input "pen" to write or draw on the screen. In all of these applications, a sampling circuit is used to detect sample and translate the touch screen input into digital signals for appropriate processing by the computer.
In general, the touch screen input sampling circuit is designed to detect and periodically sample the points at which the user's finger or pen impacts the screen and to convert each sample point into a digital value which is delivered to the microprocessor for appropriate processing. The sample points may be detected through a variety of known techniques corresponding to the different types of currently available touch screen technologies (e.g., resistive, capacitive, force vector, guided acoustic wave, surface acoustic wave, scanning infrared or strain gauge). For example, in many conventional sampling circuits the sample points are detected by pressure sensors connected to the display screen. More recently, electromagnetic sensors have been used for this purpose. Regardless of the detection method and depending on the particular application, the microprocessor may store the input values (data) for subsequent processing (e.g., when the user is entering a drawing) or immediately execute one or more functions corresponding to these values (e.g., where the user has pushed a button representing a certain command).
It is well known in the art that in order to improve the quality or reliability of the touch screen input data, the sampling rate (sampling frequency) must be increased in the sampling circuit. However, it is also recognized that a faster sampling rate leads to greater power consumption in the sampling circuit and to lower overall performance for the microprocessor as more processing cycles are devoted to handling touch screen input data as opposed to other required or desirable tasks. Thus, in some prior art portable computers a high sampling rate was used at the expense of higher power consumption and lower processor performance, while in other prior art computers, a low sampling rate was used at the expense of lower quality or insufficient data. In still other cases, a combination of both approaches was used in which the computer initially would be placed in a "sleep mode" (low sampling rate and low power consumption) and then switched to "active mode" (high sampling rate and high power consumption) once a touch screen input was detected. However, this combined approach fails to solve the problem of minimizing power consumption during active mode.
As portable computers frequently run on battery power and as battery life is limited by power consumption, it is desirable that the power consumption of the touch screen input sampling circuit be reduced to the extent possible. However, it is also desirable that the touch screen input data be as reliable as possible, which may require a higher sampling rate resulting in higher power consumption as well as lower processor performance. A primary object of the present invention is to dynamically achieve the desired tradeoff between a higher sampling rate, on the one hand, and higher power consumption and lower processor performance, on the other hand.